In the fields of material handling and industrial processing, automated equipment is used to transport loads automatically through various processing steps. As the load moves on the transportation system, it is often necessary to associate data with the load which cannot be done by applying the data to the load and by examining the load with sensors to retrieve the data. Examples of this kind of information are date of manufacture, processing steps required, ownership of the load, and cost of the load.
A typical industrial system consists of transportation elements, processing elements, operator interface elements, and data processing elements. These elements are typically arranged in a distributed and/or hierarchical manner. One conventional system consists of at least one source processing station and one destination processing station and a conveyor between the stations. In such a system each of the processing stations has an independent controller and the conveyor is independently controlled.
The source station produces loads which are carried by the conveyor to the destination station. The operation at the destination station on a particular load depends on information about the load produced by the source station. This information must be presented to the destination station synchronized with the arrival of the load. This requires intensive, dynamic processing of the data handled for each load.
There are some problems associated with this synchronization requirement. The conveyor system must maintain synchronization for all of the loads in its domain simultaneously. The conveyor system must tolerate sensor errors so as to maintain synchronization. The system must also tolerate human errors, such as the removal of a load from the middle of the conveyor. Furthermore, the system must tolerate mechanical errors such as slippage or jamming of the load on the conveyor.